Two stage control instrument



April 17, 1945. a HOLMES 2,374,097

TWO STAGE CONTROL INSTRUMENT 7 Filed May 1, 1942 as -IN5ULRTION -29 INSULATIQN INVENTOR. Aiiiwl I. 1-ro1 Patented Apr. 17, 1945 TWO STAGE CONTROL INSTRUMENT Gifford 1. Holmes, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, -Minn., a corporation of Delaware Application May 1, 1942, Serial No. 441,322

15 Claims.

two stage instruments for summer and winter use.

' In heating and cooling systems adapted to work under variable load conditions, it has been found that plural stage control is the most satisfactory, both from the standpoint of economy and comfort for the occupants. Many elaborate control systems, having a large number of control positions, have accordingly been devised to fill the i need for modulating control. However, it has also been found that a simplified control having maximum and minimum load positions only will fill a large number of these needs satisfactorily.

.The two position control involves substantially decreased installation and upkeep costs, and hence has been generally accepted in the art.

A further need in the conditioning art is control of both heating and cooling for winter and summer, respectively. There are also times in the spring and fall when both heating and cooling may be needed from day to day. For this 'reason the need is felt for control means having automatic changeover from heating to cooling,

andvice versa.

.An object of this invention is to provide a plural stage control means having automatic changeover from heating to cooling control.

A further object is to provide a simple change- :over switch embodying two stage control.

Another object is to provide a simple change- .over switch embodying two' stage snap action control.

Other objects will be in part obvious or pointed ,out in the following specification and claims,

taken in view of the drawing, in which, 4

Fig. 1 is a front view of one form of my invention'using slow action switches, and

Fig. 2 is a front view of a modification thereof,

employing snap action switches. Referring now in detail to the drawings, the

reference character In designates a base. Upon the base It) is a pivot II to which a bimetallic the right and left legs thereof or the heat responsive control members 12a and [2b respectively. The bimetallic element I2 is freely piv- 'oted on the pivot I I and may rotate therearound junder the influences of temperature variations, in av manner to be more fully pointed out hereinafter. On the lower ends of the bimetallic ele- .ment i2 are secured movable contact assemblies so strip I2 is secured by means of a bracket 13." The bimetallic strip 12 is formed so as to provide rotary pivot 42.

generally indicated by the reference characters l5 and I6. The contact assembly l5 comprises two relatively stiff arms I1 and I8' having contacts thereon anda relatively flexible arm 19 having a contact on either side of the lower end thereof. The contact assembly l6 has two relatively stiff contact arms 20 and 2| having contacts thereon and a relatively flexible contact arm 22 having a contact on each side of its lower end.

Stationary contacts which cooperate with the movable contacts of the contact assembly 18 are the cold contacts 25 and 26, called cold contacts inasmuch as these contacts are engaged by the movable contacts when the thermostat is moving in cooling direction under the influence of falling temperature; When the bimetallic member 12 is heated, the hot contacts 21 and 28 are engaged by the movable contacts of the contact assembly iii. The stationary contacts 25, 26, 21, and 28 are suitably secured to brackets carried upon an insulating panel 29.

The stationary contacts for the contact assem bly [5 are cold contacts 30 and 3| which are engaged by the movable contacts when the bimetallic member I2 is cooling. Also provided are hot contacts 32 and 33 which are engaged by the movablecontacts when the bimetallic member I2 is heating.

The contacts 30, 3|, 32 and 33 are suitably mounted on brackets carried by an insulating panel 35. This panel 35 is secured to an arm 36 which is pivotall mounted upon the pivot H. A spring 31, which engages an ear 38 upon the arm 36 and an ear 39 that is struck up from the base i0, biases the arm 36 in a counter-clockwise direction. A cam surface 40 of the insulating panel 35 engages a cam 4| which is fixed to a Also secured to the pivot 42 is an adjustment dial 43. The adjustment dial 43 has indicia 44 thereon which cooperate with a pointer 45, to indicate the control setting for the device.

A plurality of biasing springs 50, 5| and 52, the latter two of which are adjustable are provided togive the proper sequence of operation to the mechanism. The tension spring is adapted to exert a biasing force tending to pivot the thermostatic element l2 in a counter-clockwise direction. Counteracting the biasing effect of the spring 50 are the expansion springs 5| and 52.

The springs 5i and 52 are of the variable tension type so that the biasing force exerted thereby is increased as the springs 5| and 52 are compressed and decreased as the springs 5| and 52 expand.

The latter springs 5i and 52 exert a biasing force tending to pivot the thermostatic element [2 in a clockwise direction and thereby tending to counteract the counter-clockwise biasing force of the tension spring 50. As shown in Figure 1 the biasing force of the spring 50 is balanced by the biasing force of the springs iiI and 52 when in the neutral position.

Upon a decrease in temperature the ends of bimetallic thermostatic element I2 will tend to spread apart. The outward warping of the ele-.

ment I2 will tend to compress the variable tension spring 52 so as to increase: the tensionflexerted thereby on the right leg in of the element I2. Thereupon the combined-tensionexerted by the springs 5| and.52 in a clockwise direction will 5| will exceed that exerted by the relatively expanded spring 52 so that upon the outward warpingof the element I2 in response toa temperasprings 5| and 52 will tend to pivot the element tend to exceed that of the tension spring 50in s a counter-clockwise direction causing a gradual a pivoting of the element I 2 in a clockwise direction tending towards balancing the biasing efl'ects exerted by the spring elements 50', 5| and 52 as the thermostatic element I2 continues to warp outwardly until the clockwise movement of the element I2 is limited at the left leg I26 by the switch member 30 previously described. v I

Upon the limiting of the clockwise movement of the element I2 the right leg I2h of theelement I 2 will warp outwardly upon a further decrease in temperature until limited by the switch element25. 2 W

. Now with theelement I2 in the latter position engaging the switch elements as described, upon an increase in temperature the legs I2a and I 2b of the element I2 will tend to converge or warp inwardly so that the element I2 under the biasing force of the increased tension of-thecompressed spring 52 and spring 5| will be gradually pivoted clockwise on the pivot II against the tension of the spring 50. Howeversince the leftleg I21) of the elementl 2 is limited by the switch element 30 as previously noted the effect of such inward warping of the element I2 and biasing force of spring 52 will be to cause the 'right leg In of the element I 2 to break from the switch element 25. Moreover as the increase in temperature continues the inward movementpf the right leg I2a of the element I2 will reach a point where the tension exerted by the variable tension spring 52 will bedecreased by the expansionthereof to such an extent-that the combined force of the springs 5| and 52 will merely balance thepositively directed, tension ,force of the spring 50. Further inward warping of the element I2 will then cause the left leg I 2b .of the element I 2 to break from the switch element 30 and cause the gradual counter-clockwise movement of the element I2 under tension of the spring 50 tending thereby to balance the tension forces-exertedon the element I2 by the combined biasing Iorce of the variable tension sprin'gs El, and 52 until the element I2 is once again returned to the balanced neutral position indicated inFigure 1. A

Upon a further increase in temperature the inward warping of the element I2 willcohtinuecausing an increase in the tension exerted on the left leg I2b of the element -,I2 by the variable tension spring 5I' so that the combined iorce exerted by the springs 5| and 52 will tend to cause the gradual clockwisernovement of the element I2 against the counter-clockwise biasing force of the spring 50 until the right leg I2a of the element I2 is limited by the switch element 21. Upon further increase in temperature the left leg I2bof the element I2 will be warned inwardly until limited in turn by-the switch .ele ment 32. Such inward warping of the element I2 will compress-the variable tension spring 5| causing an increase in the tension exerted, thereby. -Thus upon a decrease. .inthe temperature.

the tension exerted by the varrble tensionspriiig ance the counteracting force of the tension spring 50. Further outward Warping 'of the element 12 in response to a decrease in temperature will then cause the right legv I 2a of the element I2 to break from the switch element 2'! in response to the gradual counter-clockwise movement of the element "I2 under the tension force exerted by the spring 50. Such tension will tendto position the element I2 so as to balance the tension "forces exerted .by the variable tension springs SI and 52 and the tension spring 50. The element I2 will continue in a counter-clockwise direction as the temperature decreases untilthe same is 130.- s'itioned in the balanced or neutral position such as indicated in Figure 1.

The aforenoted sequence of operation of my invention isfor the purposes which will be'he'reinafter fully pointed out in cohhetztibn with the operation of the device. '1

' Operation of Figure 1 ,toward the stationary contacts 30 and 3|. As is shown by thespac'in'g of the contacts in the drawing, the contact carried by the flexible arm I9 will first engage thefstationary contact 3|. Upon a further decrease in temperature; the flexible arm I9 will be pressed back and the ,movable contact carried by the relatively s'tifi arm I1 will engage the contact 30. In a conventional control system, not shown, when thecontact 3| was engaged no control function would be performed,'but whe'n'the contact 30 hasiengag'ed its contact a relay or other device would be energized and a holding circuit for such device would be established through the stationary contact 31. Such control systems are well known in theart and therefore have not been disclosed as they the relatively stiff member I7, the spring'52 will "now be compressed by the cooling action on the bimetal. Hence, upon further cooling the stationary contact '26 at the opposite end of the biinetal will be engaged by the contact carried-by cooling of the' bimetal the stationarycontact 25 will be engaged by the con-tact on contact arm 2|. Engagementof both stationary contacts 25 and 26 may energize a circuit for a control device similar to that pointed. out hereinbefore.

In applying the present device to a two-stage heating operation, the stationary contacts 30 and 3| would control a system at a low stage of operation. In the event that this heating system were not suificient to raise the temperature in the space to which the thermosat I2 responds, then the thermostat would further cool and cause the stationary contacts 25 and 26 to engage. At this time, a larger capacity heater would be brought on" which would cause the thermostat I2 to soon become satisfied.

When the system is operating on the cooling cycle, the action of the thermostat I2 is substantially the same as pointed out before in describing the heating operation. That is, as the thermostat I2 is subjected to higher temperature the ends of the bimetallic element I2 tend to move closer together. At this time the adjustable spring 5| resists movement of the left hand leg of the bimetal I2 but the lower right hand end thereof is free to move toward the left. As it moves toward the left the'movable contacts of the structure It engage their respective stationary contacts 21 and 23 to energize a first stage cooling means. Upon further heating of the bimetallic element I2, the element will rotate upon the pivot II and the switch contact 2! to cause the element I2 to overcome the tension of spring 5I to cause the movable contacts on the arms I8 ing member 35 to be moved in one direction or the other to bodily IPOSitiOIl the stationary contacts 30, 3I, 32 and 33. It will be obvious that when these contacts are positioned that the control setting of the device is changed inasmuch as the legs of the bimetal element I2 will need to take a different position to cause the device to be in its neutral position.

Structure of Figure 2 'Now the structure shown in Figure 2 will be described. The base III has a pivot II thereon to which the'bimetallic member I2 is secured by the bracket I3. This structure is identical to the structure disclosed in Figure 1. Likewise, the adjustment structure comprising the rotatable pivot 42 having cam 4i and the adjustment dial 43 thereon are also identical. .An adjustment arm I35 takes a slightly different form than the adjustment arm disclosed in Figure 1. The adjustment arm I33 has an ear I38 thereon which is connected to the tension spring 31 which is in turn connected to the stuck-up ear 39 on the base III. The spring 31 biases the arm I36 so that the lower end thereof will engage the adjustment cam 4 I, not shown.

A plurality of snap action switches 63 and I0 control some suitable heating means, not shown. Apluralityof switches 80 and 93 control a cooling means, .not shown. .The switches III and 90 are mounted upon the adjustment arm I36 and may be moved to vary the control setting for the thermostatic element I2 in a manner similar to the operation of setting the control point described in connection with Figure 1.

Each of the control switches 60, I0, and is similarly constructed. For this reason, only one of them will be described in detail. The switch ID has a stationary contact II cooperable with a movable contact I2-that is carried upon an arm I3 which is pivoted at I4. A spring I5 biases the arm I3 toward the right at all times. A push button I6 engages the lower left hand end of the bimetallic element I2. The push button I3 is secured to a spring II which engages the inner side of a cup I8. When the lower left hand end of the bimetallic element I2 moves towards the left the spring I! is compressed a sufficient amount to overcome the tension of the spring I5 at which-time the arm I3 will begin to move toward the left. As is shown in the drawing as the arm I3 rotates towards the left the angle between it and the line of force exerted by the spring I5 will decrease. In the structure shown it is desired that the effective force exerted on the arm I3 by the spring I5 will decrease at a more rapid rate than the force stored up in the spring II to give a spring rate compensation snap action to the switch contact I2. It will be understood, however, that other snap action devices could be utilized.

The spring I5 of the switch III is of slightly lightertension than the spring 65 of the switch 60. By such structure the switch It will be the first one to snap upon cooling movement of the bimetallic member I2, in a manner to be more fully described hereinafter. Similarly the spring 85 of the switch 33 is weaker than the spring of the switch 90.

Operation of Figure 2 In response to a decrease in temperature the distal ends of the bimetallic member I2 will tend to spread apart. Upon spreading apart the lower right hand end will tend to snap the switch 63 and the lower left hand end will tend to snap the switch III. However, .because spring 65 of switch 60 is stronger than the spring I5 of switch III the bimetallic member I2 will bear against the snapping pin of the switch 50 and compress the spring I 8 of switch 70 to such an extent that the switch III will snap and the contacts II and I2 will engage. Inasmuch as contacts II and I2 engage first these would accordingly be connected to a first stage conditioning means, not shown. Upon further cooling of the medium surrounding the bimetallic member I2, the lower left hand end thereof would bear against the switch actuating pin I6 and rotate about the pivot II to cause the lower right hand leg of the switch to move toward the right and compress and actuate the switch 63. The switch 30 might control a maximum stage heating means.

When operating on the cooling cycle the operation of .the device would. be identical to that described in connection with heating. That is, when the bimetallic member I2 is subjected to a rise in temperature the ends of the bimetallic member would tend to move toward each other. As they move toward each other the force exerted by the bimetal would act on the spring 95 of the switch 93 and spring 85 of the switch 80. Inasmuch as the spring 85 is weaker than the spring 95 the first switch to snap would be the switch 80. The switch 83 might bring on a minimum capacity cooling means. Upon further heating of the bimetal the bimetallic member I2 sprin 95 the n w l be t e first to snap ed and the switch 80 havinathe w aker spring the ein will be second t s ap t n posit n.

While I have d scri d two forms whi h my inventionmay take it wil be cl arly u d rstood that those skilled in the art will devise many modifications thereof. For example, it would be obvious to substitute magnetic snap action switches for my spring rate compensated snap action switches, or to substitute over-center snap action switches. Also,,in connection with that type of structure shown in Figure 1 it would be obviousto eliminate certain of the contacts, or to addmore contacts thereto if desired. Li ewise it will be obvious to those skilled in the art to employ the present device to control pneumatic systems, valves, and the like. For this reason I wish not to be limited in my invention only to those forms shown and described but by the spirit and scope of the appended claims.

I claim as my invention:

1. In an apparatus of the character described, comprising in combination, thermostatic means including first and second portions, each of the portions being movable in a first sense upon heating and in a second sense upon cooling, first control means actuated by the first portion as it moves in the first sense, second control means actuated by the second portion as .it moves in the first sense, third control means actuated by the second portion as it moves in the second sense and fourth control means actuated by the first portion as it moves in the second sense, and means for actuating said thermostatic means so as to cause the return of said'portions to a neutral position at a predetermined temperature.

2. A control device comprising in combination, a base, a pivot on said base, an elongated bimetal ends upon said pivot, said strip being movable in afirst sense upon heating and in a second sense .upon cooling, first and second electrical contacts actuated by said strip as it moves in said first .45 strip pivotally mounted at a point between its sense, third and fourth electrical contacts aotu- 1 ated thereafter by said strip as it continues to move in said first sense, fifth and sixth electrical contacts actuated by said strip as it moves in said second sense, and seventh and eight electrical contacts actuated thereafter by said strip as it continues to move in said second sense.

3. A control device comprising in combination a base, a pivot on said base, a variable condition responsive control member pivotally mounted at a point between its ends upon said pivot, the said control member being movable in a first sense upon heating and in a second sense upon cooling, first and second electric-contact means actuated by the said control member as it moves in said prior to said second contact means, and second 1 resilient means associated with said control memberfor causing said third contact means to be actuated prior to said fourth contact means. 4. A control device comprising in combinati n a ba epi ot on. sa d basaa ariable condition re ponsive c ntrol m mber p ota ly mounted at a point between its ends upon Said pivot, the said control member being movable .in' a first sense upon heating and in a secon sense upon coo g. fi st'and second electric contact meansactuated by the said control member as it moves in said first sense, and third and fourth electric contact means actuated by the said control member as it moves in said second sense, and first resilient means associated with said control member for causing said first contact means to be actuated prior to said second contact means, second resilient means associated with said control member for causing said third contact means to be actuated prior to said fourth contact means, and a, third resilient means associated with said control memher for returning the said control member to a neutral position at a predetermined temperature.

5. A control device comprising in combination, a base, a pivot on said base, an elongated bimetal strip pivotally mounted at a point (between its ends upon said pivot, said strip being movable in a first sense upon heating and in a thereafter as said strip continues to move in said" second sense.

6. 'A control device comprising in combine.- tionja base, a pivot on said base, an elongated bimetal strip pivotally mounted at a point between its end upon said pivot, said strip being movable in a; first sense upon heating and in a second sense upon cooling, a plurality of pairs of snap action switching means adjacent the ends of said strip, relatively weak spring means associated with one pair of said switching means, andtrelatively strong spring means associate with a second pair of said switch means, said strip bearing upon one of said stronger springs and rotating upon said pivot to overcome one of said weaker springs to providea first stage snap action and rotating upon said pivot while bearing upon the contacts associated V with said weaker spring to overcome the force of said stron er spring to provide a second stage snap action, as the strip moves in either or its senses.

7. In an apparatu of the character described, comprising, combination, heat responsive mean including first and second portions, each of the portions being movable in a first sense upon heating and in a second senseupon cool-, ing, first control means actuated by the first portion as it moves in the first sense, second control means actuated by the second portion as" it moves in the first sense at a temperature above the temperture at which the said first control means is actuated, third control means actuated by the second .portion as it moves in actuating the third control- 8. In an apparatus of the character described, comprising, in combination, heat responsive means including first and second portions, each of the portions being movable in a first sense upon heating and in a second sense upon cooling, first control means actuated by the first portion as it moves in the first sense, second control means actuated by the second portion as it moves in the first sense at a temperature above the temperature at which the said first control means is actuated, third control means actuated by the second portion as it moves in the second sense. fourth control means actuated by the first portion as it moves in the second sense at a temperature below the temperature at which the sai third control means is actuated, and biasing means for preventing the actuation of the second control means upon the first portion actuating the first control means.

9. In an apparatus of the character described. comprising, in combination, heat responsive means including first and second portions, each of the portions being movable in a first sense upon heating and in a second sense upon cooling, first control means actuated by the first portion as it moves in the first sense, second control means actuated by the second portion as it moves in the first sense at a temperature above the temperature at which the said first control means is actuated, then third control means actuated by the second portion as it moves in the second sense, fourth control means actuated by the first portion as it moves in the second sense at a temperature below the temperature at which the said third control means is actuated, and biasing means actuating the heat responsive means in such a manner as to return said portions thereof to a neutral position at a predetermined temperature.

10. In combination, a freely pivoted distortable thermal means having two spaced movable portions, each of the said portions of the thermal means being movable in a first sense upon heating and in a second sense upon cooling, control means engaged by the said portions of the thermal means as the said portions move in the first sense, and other control means engaged by the said portions of the thermal means as the said portions move in the second sense.

11. In combination, a freely pivoted distortable thermal means having two spaced movable portions, each of the said portions of the thermal means being movable in a first sense upon heating and in a second sense upon cooling, control means engaged by the said portions of the thermal means as the said portions move in the first sense and other control means engaged by the said portions of the thermal means as the said portions move in the second sense, and tension means whereby the said portions of the thermal means are positioned in such a manner as to disengage all of the said control means at a predetermined temperature.

12. In combination, a base, an expansible member mounted thereon in a manner to permit movement of each end of said member upon expansive and contractive movements thereof, a first pair of devices of which one is operated by each end of said member upon expansive movement of said member, a second pair of devices of which one is operated by each end of said member upon contractive movement of said member, one of each of said pairs of devices acting as a means to constrain further movement of that end of the member which operates it so that further movement of said member is imparted solely to the other end thereof so as to operate the other of said pair of devices.

13. In combination, a base, an expansible member mounted thereon in a manner to permit movement of each end of said member upon expansive and contractive movements thereof, a first pair of devices of which one is operated by each end of said member upon expansive movement of said member, a second pair of devices of which one is operated by each end of said member upon contractive movement of said member, means to constrain expansive movement of one end of said member so that the other end thereof moves first to operate its one of the first pair of devices after which the second of said first pair of devices is operated by the other end of said member upon further expansive movement thereof, and means to constrain the contractive movement of one end of said member so that the other end thereof moves first to operate its one of the second pair of devices after which the second of said second pair of devices is operated by the other end of said member upon further contractive movement thereof.

14. In an apparatus of the character described, comprising, in combination, heat responsive means including first and second portions, each of the portions being movable in a first sense upon heating and in a second sense upon cooling, first control means actuated by the first portion as it moves in the first sense, second control means actuated by the second portion as it moves in the first sense at a temperature above the temperature at which the said first control means is actuated, third control means actuated by the second portion as it moves in the second sense, fourth control means actuated by the first por- 0 tion as it moves in the second sense at a temperature below the temperature at which the said third control means is actuated, biasing means for preventing the actuation of the second control means upon the first portion actuatin the first control means, biasing means for preventing the actuation of the fourth control means upon the second portion actuating the third control means, and biasing means actuating the heat responsive means in such a manner as to return said portions thereof to a neutral position at a predetermined temperature.

15. In an apparatus of the character described, comprising, in combination, heat responsive means including first and second portions, each of the portions being movable in a first sense upon heating and in a second sense upon cooling, first control means actuated by said first portion as it moves in the first sense, second control means actuated by the second portion as it moves in the first sense at a temperature above the temperature at which the said first control means is actuated, third control means actuated by the second portion as it moves in the second sense, fourth control means actuated by the first portion as it moves inthe second sense at a temperature below the temperature at which the said third control means is actuated, biasing means for preventing the actuation of the second control means upon the first portion actuating the first control means, and biasing means for preventing the actuation of the fourth control means upon the second portion actuating the third control means.

GIFFORD I. HOLMES. 

